Ok, I have been threatening to do this for a longtime, so here it is finally. A few weeks ago I ordered a set of 3.91s and a Harrop cover for my GTO. I decided that I was going to do a step by step how-to on the rearend removal and eventually the gear installation.

Pic of the car on jackstands, exhaust already removed:

Here is a pic of the tools you will need, a rachet with an 18mm socket, a medium sized adjustable wrench (or an 18mm wrench, I didn't have one handy), a 15mm wrench, a 17mm wrench (and another one to use as a cheater), another rachet with short extension and a 13mm, 14mm and a 15mm DEEP socket, an 8mm allen and a 5mm allen:

You will also need a foor jack and some jack stands.

In this pic, you can see the torx head bolts on the pinion flange. I do not know what size these are exactly, but a 12 point 14mm socket it fits it perfectly. Works good. You will have to remove all 6 of these bolts. 3 have the torx heads and the other three are 18mm with locking nuts on the back side. The center support for the driveshaft has two 13mm bolts. Once all the bolts on the pinion flange are removed and the center support mount bolts, the entire shaft can be removed. You have to wrestle with it a bit to get it past the nipple on the pinion gear, but it'll come. You need to force it forward as much as it will go once its unbolted from the pinion flange.

Here are the forward (upper) mount bolts. There are two, they are 17mm. It is easier to get to them after the driveshaft has been removed. I used a regular 17mm wrench with an 11/16 doubled on it as a cheater.

There are a total of FOUR of these bolts on top of the rear subframe. The rear upper two can't really be seen until you unbolt the rear mount and let the entire assembly down. Then you can get to them, also 17mm. I used the same double wrench technique to get them loose. You have to have all four of these bolts out and the four bolts that hold the rear mount in place in order to get the rearend out. There's also a vent pipe up on top that you will have to disconnect. Below is a pic of the rear mount, the four bolts are 13mm:

Next, you have to remove the antilock brake sensors and unbolt the half shafts from the stub axles. The ABS sensors have a single 5mm allen holding them in and the half shaft bolts are 8mm allens.

Now, once you have all this unbolted you can easily remove the rearend. Keep in mind that you will need to keep it supported on a floor jack while unbolting the mounts. I unbolted the half shafts and all the other stuff first, then did the mounts last. Unbolt the forward upper mounts first, then the rear mount, then you can let it down to get to the top rear mount bolts. Once they are out, it'll come on out. This job took me 45 mins from start to finish and that included removing the exhaust.

Changing the final drive gear ratio is the single biggest improvement you can make to the "seat of your pants" feel of your car. Going from a 3.46:1 to a 3.91:1 ratio will give the engine a better mechanical advantage on the rear wheels and also relieve stress from the clutch, transmission and driveshaft. (Increases stress on the axles). In other words...instead of only being able to spin through 2nd gear, I should now be able to continue spinning well into 3rd gear. lol. Get it?

wow so it sounds like the engine in a way got more "grip" on those wheels to project power, am i wording this correctly? hows your milage going to be? also does that shave off some time on the 1/4 mile?

I want to go the other way, and up the ratio to about a 3:07 with my automatic. How about swapping in a complete third member? If you don't mind, what did the gears cost, I haven't seen them advertised.

I want to go the other way, and up the ratio to about a 3:07 with my automatic. How about swapping in a complete third member? If you don't mind, what did the gears cost, I haven't seen them advertised.

Gears are expensive. And I assume that you have no intentions of increasing performance with 3.07 gears...yuck. You'll spend at least $600 on the gearset, no matter what the ratio.

The AutoGuide.com network consists of the largest network of enthusiast-owned enthusiast-operated automotive communities.

AutoGuide.com provides the latest car reviews, auto show coverage, new car prices, and automotive news. The AutoGuide network operates more than 100 automotive forums where our users consult peers for shopping information and advice, and share opinions as a community.